Electric-Field-Induced Tautomerism in Metal-Free Benziporphyrins Enables Aromaticity-Controlled Conductance Switching

TL;DR

This paper introduces metal-free benziporphyrins that can switch between different tautomeric states under an electric field, enabling high-contrast conductance switching for molecular electronics applications.

Contribution

The study presents a new class of molecules, MFBPs, with tunable tautomeric states controlled by electric fields, advancing the design of molecular switches and memory devices.

Findings

Electric fields can selectively stabilize each tautomer.

Each tautomer exhibits distinct conductance profiles.

ON/OFF ratios exceed 500 at low bias.

Abstract

Metal-free porphyrins can switch between hydrogen-bonded tautomers, potentially enabling reversible control in molecular electronics. However, electric field gating of porphyrin tautomerism, which is critical for device integration, has not been fully realized. We propose metal-free benziporphyrins (MFBPs), in which one pyrrole ring is replaced with a phenol group, as a new platform for tautomer-based molecular electronics. This approach introduces asymmetry, which allows for three distinct tautomers, each possessing a characteristic aromatic or antiaromatic electronic structure. Density functional theory and quantum transport calculations show that: i) experimentally realisable electric fields can selectively stabilize each tautomer, and ii) each tautomer exhibits a characteristic conductance profile. The strong switching capability of MFBPs is demonstrated by ON/OFF ratios exceeding 500 at low bias. Fused MFBPs further expand functionality by providing multiple tautomeric states for multistate molecular registers and enabling wire-like architectures with enhanced conductance. These results establish MFBPs as versatile building blocks for electric-field-responsive molecular devices and open new research opportunities for molecular-scale logic and memory.